You have no doubt heard a lot of buzz about a concept called Web 2.0 bandied about by Silicon Valley marketers, bloggers, and pundits of all stripes. So what is it?

A universally agreed-upon definition hasn't yet arisen. Presented with the question, programmers will launch into long-winded explanations that include terms like Ajax and Web services. Microsoft haters will say it replaces the desktop as a platform for computing. Marketers will emphasize the "richness" of the user experience. The digerati -- technology-oriented yuppies who work in San Francisco and New York brick lofts and are as addicted to buzzwords as they are to Peet's coffee -- will go on about "wikis" and "mashups" and "memes" and the "granular addressability of content."

		15 Years Of The World Wide Web
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Which brings us back to the question: What is Web 2.0? Here's my plain-vanilla definition: Web 2.0 is all the Web sites out there that get their value from the actions of users.

To illustrate this concept: Yahoo News features both old-school Web mechanisms and Web 2.0 components. Comparing the two shows the stark difference between Web 1.0 and Web 2.0 approaches to creating value.

Yahoo's Top Stories page lists articles according to what editors think should be on the page -- and in what order. The value of the page is provided by the judgment of professionals. But Yahoo's Most Emailed News page places and ranks stories based on the actions of users: Those stories that are e-mailed the most rise to the top. It's a Web 2.0 concept. The value of the page is derived from the actions of users.

Flickr: We know Web 2.0 when we see it.

Here are some perfect examples of Web 2.0 sites:

• Wikipedia: An online encyclopedia written and edited (and re-edited and re-edited) by its users.

• Digg: A social bookmarking site where users post story links and vote for, or "digg," stories posted by others. Those with the most votes make it to the home page, so visitors to that page see only the most popular stories. (Or not -- there have recently been accusations that Digg's system is being manipulated by a small group of users.)

• Technorati: A blog search engine that ranks blogs according to how many other blogs link to them.

• Flickr: A site where anyone can post and share pictures, which can be browsed by anyone else with help from popularity rankings.

  Map your friends with Frappr.

• Frappr: A mashup, or combination of two sources of data, that lets you show the locations of the members of any group on a Google Maps map.

Those are purely Web 2.0 sites. They were preceded by quasi-Web 2.0 sites -- let's call them Web 1.5 sites -- that you'll be very familiar with:

• Amazon.com: Gets part of its value from reviews written and ranked by users.

• Google: Gets part of its value from ranking Web sites according to how many other Web sites (and which ones) link to those sites.

• Rotten Tomatoes: Gets most of its value from a ranking system that gives the collective opinion of movie reviewers, but also lets people create journals and rank movies according to what their friends think.

For more examples of Web 2.0 sites, check out Seth Godin's Web 2.0 Traffic Watch List and All Things Web 2.0.

So there you have it. A workable (if oversimplified) definition of Web 2.0. Ultimately, however, labels are of little value. The bottom line is that radical innovation is alive and well on the Internet. It's a great time to be surfing the Web.